Disk drives are an important data storage technology, which is based on several crucial components. These components include the interconnection between the read/write heads, which actually communicate with a disk surface containing the data storage medium, and the read/write interfaces of the disk drive. While there has been great progress in disk drives, there are problems which have yet to be solved.
FIG. 1A illustrates a typical prior art high capacity disk drive 10 including actuator arm 30 with voice coil 32, actuator axis 40, suspension or head arms 50-58 with slider/head unit 60 placed among the disks.
FIG. 1B illustrates a typical prior art high capacity disk drive 10 with actuator 20 including actuator arm 30 with voice coil 32, actuator axis 40, head arms 50-56 and slider/head units 60-66 with the disks removed.
Since the 1980's, high capacity disk drives 10 have used voice coil actuators 20-66 to position their read/write heads over specific tracks. The heads are mounted on head sliders 60-66, which float a small distance off the disk drive surface when in operation. Often there is one head per head slider for a given disk drive surface. There are usually multiple heads in a single disk drive, but for economic reasons, usually only one voice coil actuator.
Voice coil actuators are further composed of a fixed magnet actuator 20 interacting with a time varying electromagnetic field induced by voice coil 32 to provide a lever action via actuator axis 40. The lever action acts to move head arms 50-56 positioning head slider units 60-66 over specific tracks with remarkable speed and accuracy. Actuator arms 30 are often considered to include voice coil 32, actuator axis 40, head arms 50-56 and head sliders 60-66. Note that actuator arms 30 may have as few as a single head arm 50. Note also that a single head arm 52 may connect with two head sliders 62 and 64.
The evolution of disk drives stimulated the computer revolution. While contemporary actuator designs are essential to the progress to date, there remain problems limiting the reliability and capability of disk drives built with contemporary voice actuators. One problem has to do with the method of electrically interconnecting heads to the head interface electronics.
FIGS. 2A, 2B, 2C and 2D illustrate a prior art actuator arm from the top view, detailed portion of top view, side view and front views, respectively.
FIG. 2A illustrates a top view of a prior art actuator arm 30 showing head arm 50, actuator axis 40, and head slider 60 of FIG. 1 with detail region 70 illustrated in FIG. 2B.
FIG. 2B illustrates a top view of detail region 70 of FIG. 2A.
FIG. 2C illustrates a side view of part of detail region 70 of FIG. 2B indicating the interconnections 74-80 via various head sliders as found in the prior art. Each of these labeled interconnections includes two pairs of differential signals. One differential signal pair interconnects a read head to a read interface of the disk drive. The other differential signal pair interconnects a write head to a disk drive write interface.
FIG. 2D illustrates a different perspective on FIG. 2C, illustrating that these signal interconnections 74 may be embodied as various forms of cables attached to a head arm, including flex and ribbon cables.
FIG. 2E illustrates an alternative prior art electrical interconnection scheme for 74-80 essentially parallel to head arm 50. FIG. 2E is typical of prior art uses of flex circuitry to interconnect head sliders and disk read/write interfaces. Four individual traces are used for the read differential signal pair (R+, R−) and the write differential signal pair (W+, W−).
FIG. 2F illustrates a typical signal strength situation between a write differential signal pair and a read differential signal pair.
All of the known prior art face similar circuit situations, leading to a common problem. The differential signal traces are situated at differing distances from the ground plane, which runs through the head arms. Additionally, the differential signal traces are often not parallel to each other within the pair. These two situations lead differing differential signal pairs to have impedance mismatches, creating significant crosstalk between them.
Crosstalk is a function of both the distance between traces D, and the distance from the ground plane H. Crosstalk is proportional to 1/ (1+(D/H)^2).
Most importantly, the write differential signal pairs induce crosstalk on the read signal pair. This added noise limits the frequency at which the heads can be sensed and controlled. It also limits the reliability of the disk drive as a whole, reducing its life expectancy. This reduction in life expectancy is a cumulative effect of this noise, heating while the disk drive is operating and cooling when the disk drive is turned off.